This invention relates to X-ray photographing apparatus and in particular to X-ray photographing apparatus including an X-ray shielding means.
As a prior art X-ray photographing apparatus a computed tomography is known which is adapted to expose a to-be-examined subject with an X-ray pulse beam, detect an X-ray beam portion penetrated through the subject, reconstitute the data of the detector by a computer and display as a tomographing image on a display the X-ray absorption coefficient of each part of the subject. There is also known a "cinecardioangiographing" apparatus (usually referred to as "cineangio") which is adapted to expose a subject with an X-ray pulse beam, after a contrast medium is injected into the blood vessel of the subject, and to photograph an X-ray pulse beam portion, by a cinecamera, which is penetrated through the subject.
In the above-mentioned X-ray photographing apparatus, pre-exposure is effected once a day before use to remove an initial X-ray output variation involved when X-ray exposure is started. When, however, the apparatus is repeatedly operated, such an initial X-ray output variation could not always be removed by a once-per-day pre-exposure. When pre-exposure is effected for each operation, a dissipation power is increased and a diagnosis processing capability is lowered. In this way, the conventional computed tomography requires a number of pre-exposures and it also requires a constant X-ray output. An initial X-ray output variation results in the degradation of a tomographing image on a display. Such initial X-ray output variation is removed in the conventional apparatus by detecting by means of a reference detector the intensity of X-ray pulse beam before its transmission through a subject, comparing the intensity of the X-ray beam before its transmission through the subject and the intensity of the X-ray beam after its transmission through the subject and removing some of the X-ray intensity variation. Since, however, two detectors used before and after the transmission of the X-ray beam through the subject, each, have a different characteristic, it is not sufficient in the conventional apparatus to completely remove an initial X-ray output variation.